1. Field of the Invention
The present invention relates to an imaging apparatus such as a digital still camera or a digital video camera (referred to as “digital camera”, hereinafter) and the like, which has an image blur correction function for correcting image blur when photographing.
2. Description of the Related Art
In an imaging apparatus having a photographing lens system (photographing optical system) configured to image a subject image and an image pickup device (CCD, or the like) configured to receive the subject image obtained through the photographing lens system and to output an image signal, a digital image corresponding to the subject image based on the output image signal is generated. As such an imaging apparatus, recently, a digital camera having a so-called image blur correction function for correcting an image blur occurring when photographing has been in practical use.
As such an image blur correction means, structure in which, for example, the image pickup device such as a CCD or the like is moved in a plane (an X-Y plane) perpendicular to an optical axis (in a Z axis direction) of the photographing optical system is employed (see Japanese Patent Application Publication No. 2001-066655). In the digital camera having the conventional image blur correction function, the CCD as the image pickup device is mounted on a mounting stage provided at an end of a fixation cylinder housing a lens barrel on a photographing optical axis. This mounting stage is provided movably in the X-Y plane perpendicular to the photographing optical axis as the Z axis direction. The mounting stage is movable due to magnetic forces generated by a permanent magnet and a coil facing the permanent magnet. In the conventional digital camera, a camera shake detection sensor detects inclinations in relation to directions of a Y axis and an X axis, respectively and an electrical current applied to the coil is controlled to be changed based on detection outputs of the camera shake detection sensor so that the CCD is moved so as to follow a movement of the subject image due to camera shake.
In the conventional digital camera, an original position is set to a position on the photographing optical axis (Z axis) within a movable range of the mounting stage on which the CCD is mounted. The CCD is moved to follow the movement of the subject image due to camera shake on a basis of the original position as a reference position so that an appropriate image blur correction can be achieved while degrade of the image is prevented. Therefore, when the image blur correction is started, it is preferable that the CCD is positioned at the original position. At this time, the movable range of the mounting stage is essentially finite and therefore the original position as the reference position is set to be matched with a center position of the movable range of the mounting stage so that a wider range image blur correction can be achieved.
When the image blur correction is not operated, it is possible that the CCD is constantly positioned to the original position, that is, the center position of the mounting stage by use of the magnetic force of the permanent magnet and the coil. That is, the image pickup device is electrically held at the original position by the magnetic force of the permanent magnet and the coil (referred to as electrically holding or electrically holding state, hereinafter). However, in this case, it is necessary to continuously apply electrical current to the coil, and therefore there is room for improvement in reduction of a power consumption.
In the camera having the image blur correction function, it is proposed that the mounting stage is mounted on a back surface of the fixation cylinder by use of a pitch coil spring so as to movable in the X-Y plane. In this case, a position in which a spring force of the pitch coil spring and a force of gravity on the mounting stage are equal to each other is set to a starting position of the image blur correction. That is, the image pickup device is mechanically held at a held position by a biasing force of the spring, or the like (referred to as mechanically holding or mechanically holding state, hereinafter) (see Japanese Patent Number 3188739). In this case, the mechanically holding is constantly performed and after a holding state of the image pickup device is changed from the mechanically holding to the electrically holding, the CCD is moved so as to follow the camera shake by use of the magnetic force of the permanent magnet and the coil. Since it is difficult to position the CCD so as to completely match the held position by the mechanically holding with the original position, it is possible that the image is deviated when the holding state is changed from the mechanically holding to the electrically holding to start the image blur correction.
It is also possible that the imaging apparatus having the image blur correction function has a forcibly-holding mechanism for mechanically holding and fixing the image pickup device at the original position (see Japanese Patent Application Publication Number 2007-102062). In this case, the power consumption can be reduced and the image deviation does not basically occur when the image blur correction starts. However, when unexpected large impact or shock is given in the mechanically holding state, the CCD is deviated from the original position and therefore it is possible that the image is deviated for a moment when the holding state is changed from the mechanically holding to the electrically holding.
Furthermore, it is possible that the imaging apparatus has the image blur correction function in which a position of the image pickup device in the electrically holding is changed in accordance with a position of the image pickup device in the mechanically holding (see Japanese Patent Number 2579035. In this case, the imaging apparatus has a means for memorizing the mechanical held position. Every time when a releasing operation and holding operation, the electrically held position of the image pickup device is changed to a position corresponding to the mechanically held position and therefore the image deviation occurring when the holding state is changed from the mechanically holding to the electrically holding is suppressed.
However, since the electrically held position is changed and therefore the starting position of the image blur correction operation, that is, the original position is changed, the original position is off from a position on the photographing optical axis (Z axis) so that it is possible that the image quality is degraded.